Gate-to-source monitoring of power switches during runtime

ABSTRACT

A driver circuit may be configured to control a power switch. The driver circuit may comprise an output pin configured to deliver signals to a gate of the power switch to control an ON/OFF state of the power switch, and a comparator configured to compare a gate-to-source voltage of the power switch to a first threshold when the power switch is ON and to compare the gate-to-source voltage of the power switch to a second threshold when the power switch is OFF.

TECHNICAL FIELD

This disclosure relates to power switches, and more specifically,techniques and circuits for monitoring the operation of power switchcircuits.

BACKGROUND

Field Effect Transistors (FETs) are often used as power switches tocontrol the delivery of power to a load. Examples of FETs may include,but are not limited to, junction field-effect transistor (JFET),metal-oxide-semiconductor FET (MOSFET), dual-gate MOSFET, any other typeof FET, or any combination of the same. Examples of MOSFETS may include,but are not limited to, PMOS, NMOS, DMOS, or any other type of MOSFET,or any combination of the same. MOSFETs may be formed in silicon,gallium nitride, silicon carbide, or other materials.

Power switches are typically controlled by a driver circuit via amodulation control signal, such as pulse width modulation (PWM), pulsefrequency modulation (PFM), pulse duration modulation, pulse densitymodulation, or another type of modulation control signal. Modulationcontrol signals can be applied to the gate of a power switch so as tocontrol on/off switching of the power switch, and thereby control theaverage amount of power delivered through the power switch to a load.The on/off switching of the power switch effectively chops its powerdelivery up into discrete parts. The average value of voltage and/orcurrent fed to a load can be controlled by turning the switch ON and OFFat a fast rate. The longer the switch is on compared to the off periods,the higher the total power supplied to the load.

In many applications, two different power switches are configured in ahigh-side and low-side configuration, and the ON-OFF switching of thetwo power switches is synchronized in order to deliver the desired powerto a switch node positioned between the high-side and low-side switch.Moreover, in some systems, different sets of high-side and low-sideswitches may be used to control different phases of a multi-phaseelectrical motor.

It is often desirable to monitor operation of power switches in order topromote safety and identify potential fault conditions.

SUMMARY

In general, this disclosure describes circuits and techniques that areapplied by a driver circuit or a system in controlling a power switchand to monitor the power switch during operation. The circuits andtechniques can facilitate gate-to-source monitoring of a power switch byusing a single comparator for the power switch in order to monitorON-OFF transitions and to separately monitor OFF-ON transitions of thepower switch during operation of the power switch. The comparator can beconfigured to compare a gate-to-source voltage of the power switch to afirst threshold when the power switch is ON and to compare thegate-to-source voltage of the power switch to a second threshold whenthe power switch is OFF. The comparator may be configurable with eitherthe first threshold or the second threshold based on one or more controlsignals from a control unit. Moreover, in some examples, the comparatorcan be configured to have a first polarity when the power switch is ONand configured to have a second polarity when the power switch is OFF,wherein the first polarity is different than the second polarity. Thepower switch may comprise a high-side power switch or a low-side powerswitch of a half bridge circuit. In some examples for a half-bridgecircuit, a first comparator may be used with the high-side power switchand second comparator may be used with the low-side power switch inorder to perform the gate-to-source monitoring for both the high-sidepower switch and the low-side power switch according to this disclosure.

In one example, this disclosure describes a driver circuit configured tocontrol a power switch, the driver circuit comprising: an output pinconfigured to deliver signals to a gate of the power switch to controlan ON/OFF state of the power switch; and a comparator configured tocompare a gate-to-source voltage of the power switch to a firstthreshold when the power switch is ON and to compare the gate-to-sourcevoltage of the power switch to a second threshold when the power switchis OFF. The comparator may be configurable with either the firstthreshold or the second threshold based on one or more control signalsfrom a control unit. In some examples, the comparator is configured tohave a first polarity when the power switch is ON and configured to havea second polarity when the power switch is OFF, wherein the firstpolarity is different than the second polarity.

In another example, this disclosure describes a system comprising: acontrol unit; and a driver circuit configured to receive control signalsfrom the control unit and to control a half-bridge based on the controlsignals, wherein the half-bridge includes a high-side power switch and alow-side power switch. In this example, the driver circuit may comprisea first output pin configured to deliver high-side signals to a gate ofthe high-side power switch to control an ON/OFF state of the high-sidepower switch and a second output pin configured to deliver low-sidesignals to a gate of the low-side power switch to control an ON/OFFstate of the low-side power switch. In addition, the driver circuit maycomprise a first comparator configured to compare a gate-to-sourcevoltage of the high-side power switch to a first threshold when thehigh-side power switch is ON and to compare the gate-to-source voltageof the high-side power switch to a second threshold when the high-sidepower switch is OFF, and a second comparator configured to compare agate-to-source voltage of the low-side power switch to the firstthreshold when the low-side power switch is ON and to compare thegate-to-source voltage of the low-side power switch to the secondthreshold when the low-side power switch is OFF.

In another example, this disclosure describes a method of controlling apower switch, whereby the method comprises delivering signals to a gateof the power switch to control an ON/OFF state of the power switch;receiving a first threshold to configure a comparator; comparing agate-to-source voltage of the power switch to the first threshold whenthe power switch is ON; receiving a second threshold to configure thecomparator, wherein the second threshold is different than the firstthreshold; and comparing the gate-to-source voltage of the power switchto the second threshold when the power switch is OFF.

Details of these and other examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a system comprising a driver circuit thatcontrols a power switch and monitors operation of the power switchaccording to this disclosure.

FIG. 2 is a block diagram of a system that includes a half-bridge drivercircuit that controls a high-side power switch and a low-side powerswitch and monitors operation of the high-side and low-side powerswitches according to this disclosure.

FIG. 3 is a circuit diagram showing three half-bridges arranged tocontrol operation of an electric motor.

FIGS. 4A-4D are timing diagrams illustrating one or more aspects of thisdisclosure.

FIGS. 5 and 6 are flow diagrams according to this disclosure.

DETAILED DESCRIPTION

This disclosure describes circuits and techniques that are applied by adriver circuit or a larger system in controlling a power switch and tomonitor the power switch during normal operation of the power switch.The circuits and techniques can facilitate gate-to-source monitoring ofa power switch by using a single comparator for the power switch inorder to monitor ON-OFF transitions and to separately monitor OFF-ONtransitions of the power switch during operation of the power switch,e.g., during each switching cycle of the power switch. The comparatorcan be configured to compare a gate-to-source voltage of the powerswitch to a first threshold when the power switch is ON and to comparethe gate-to-source voltage of the power switch to a second thresholdwhen the power switch is OFF.

The comparator may be configurable with either the first threshold orthe second threshold based on one or more control signals from a controlunit, such as a microcontroller or microprocessor. Moreover, in someexamples, the comparator can be configured to have a first polarity whenthe power switch is ON and configured to have a second polarity when thepower switch is OFF, wherein the first polarity is different than thesecond polarity. By controlling the polarity of the comparator, logicsignals from the comparator can be simplified such that the same logicsignal can be generated for identifying either latent faults duringON-OFF transitions or latent faults during OFF-ON transitions.

The power switch may comprise a high-side power switch or a low-sidepower switch of a half bridge. In some examples for a half-bridge, afirst comparator may be used with the high-side power switch and secondcomparator may be used with the low-side power switch in order toperform the gate-to-source monitoring for both the high-side powerswitch and the low-side power switch according to this disclosure. Thehalf-bridge may comprise one of several half-bridge circuits used forcontrolling an electric motor. Each phase of the electric motor may becontrolled by a half-bridge, each of the half-bridges may comprisehigh-side and low-side power switches, and each of the power switchesmay be controlled by a driver that includes a comparator for monitoringthe respective power switch according to this disclosure.

FIG. 1 is a block diagram a system 100 comprising a driver circuit 106that controls a power switch 116 and monitors operation of power switch116 using a gate-to-source comparator 110 according to this disclosure.The source, the gate, and the drain of power switch 116 are labeled inFIG. 1 .

Driver circuit 106 is configured to control power switch 116. Drivercircuit 106 comprises an output pin 112 configured to deliver signals toa gate of power switch 116 in order to control an ON/OFF state of thepower switch 116. For example, driver circuit 106 may deliver pulsemodulation signals to the gate of power switch 116 in order to controlpower switch 116 ON and OFF. The pulse modulation signals may comprisepulse width modulation (PWM) signals, pulse frequency modulation (PFM)signals, pulse duration modulation signals, pulse density modulationsignals, or other types of modulation signals for controlling powerswitches. Control unit 102 may send control signals to driver circuit106 that define the modulation signals.

As shown in FIG. 1 , driver circuit 106 includes a comparator 110 thatis configured to compare a gate-to-source voltage of power switch 116 toa first threshold (Ton) when power switch 116 is ON and to compare thegate-to-source voltage of power switch 116 to a second threshold (Toff)when the power switch 116 is OFF. By using the same comparator 110 tomonitor both the first and second thresholds at different times ofoperation, the number of comparators needed for the monitoring can bereduced relative to one or more conventional techniques. In this case,comparator 110 is configurable to apply a first threshold (Ton) when thepower switch 116 is ON and to apply a second threshold (Toff) when thepower switch 116 is OFF. For example, comparator may be configurablewith either the first threshold or the second threshold based on one ormore signals from control unit 102.

Comparator 110 may be configured to output a first logic signal inresponse to the gate-to-source voltage being greater than the firstthreshold when power switch 116 is ON and to output a second logicsignal in response to the gate-to-source voltage being less than thesecond threshold when power switch 116 is OFF. In this case, the absenceof a logic signal from comparator 110 during any switching cycle ofpower switch 116 may indicate a fault associated with comparator 110.Such a fault due to the absence of a logic signal from comparator 110during a switching cycle, for example, may be used as a self-test on theoperation of comparator 110 during operation of power switch 116, andmay be used by control unit 102 to issue a maintenance alert for thesystem 100 when a fault is identified. For example, in response toreceiving an indication of a fault from comparator 110, which maycomprise the absence of an expected logic signal, control unit 102 mayissue a maintenance alert for the system 100. In such cases, the signalsfrom comparator 110 may be identified as being unreliable.

In some examples, the polarity of comparator 110 is also configurable,e.g., based on control signals from control unit 102. By configuring andre-configuring the polarity of comparator 110, the logic signals fromcomparator 110 can be made similar for identifying both the ON state andthe OFF state of power switch 116. Comparator 110 may be configured tohave a first polarity when power switch 116 is ON and configured to havea second polarity when power switch 116 is OFF, wherein the firstpolarity is different than the second polarity. As will be described ingreater detail below, this can simplify logic signals from comparator116.

FIG. 2 is a block diagram of a system that includes a half-bridge drivercircuit 204 that controls a high-side power switch 216 and a low-sidepower switch 218 and monitors operation of high-side power switch 216and low-side power switch 218 according to this disclosure. The source,the gate, and the drain of both high-side power switch 216 and low-sidepower switch 218 are labeled in FIG. 2 .

Half-bridge driver circuit 204 includes a high-side driver 206configured to control a high-side power switch 216 and a low-side driver208 configured to control a low-side power switch 218. The half-bridgedriver circuit comprises a first output pin 212 configured to deliverhigh-side signals to a gate of high-side power switch 216 to control anON/OFF state of high-side power switch 216, and a second output pin 214configured to deliver low-side signals to a gate of low-side powerswitch 218 to control an ON/OFF state of the low-side power switch 218.A first comparator 210 is configured to compare a gate-to-source voltageof high-side power switch 216 to a first threshold when high-side powerswitch 216 is ON and to compare the gate-to-source voltage of high-sidepower switch 216 to a second threshold when high-side power switch 216is OFF. In addition, a second comparator 212 is configured to compare agate-to-source voltage of low-side power switch 218 to the firstthreshold when low-side power switch 218 is ON and to compare thegate-to-source voltage of low-side power switch 218 to the secondthreshold when the low-side power switch 218 is OFF.

Each of comparators 210 and 212 operate in a manner that is similar tooperation of comparator 110 shown in FIG. 1 . Thus, each comparator 210,212 is configurable to apply a first threshold (Ton) when the powerswitch 116 is ON and to apply a second threshold (Toff) when the powerswitch 116 is OFF. For example, each comparator 210, 212 may beconfigurable with either the first threshold or the second thresholdbased on one or more signals from control unit 202.

Each comparator 210, 212 may be configured to output a first logicsignal in response to the respective gate-to-source voltage beinggreater than the first threshold when power switch 216 or 218 is ON andto output a second logic signal in response to the respectivegate-to-source voltage being less than the second threshold when powerswitch 216 or 218 is OFF. In each case, the absence of a logic signalfrom comparator 210 or 212 during a switching cycle of power switch 216or 218 may indicate a fault associated with respective comparator 210 or212. Such a fault due to the absence of a logic signal from comparator210 or 212 during a switching cycle, for example, may be used by controlunit 202 to issue a maintenance alert for the system 200. For example,in response to receiving an indication of a fault from a comparator 210or 212, which may comprise the absence of an expected logic signal,control unit 202 may issue a maintenance alert for the system 200. Insuch cases, the signals from one or both of comparators 210, 212 may beidentified as being unreliable.

As with the example shown in FIG. 1 , in FIG. 2 , the polarity ofcomparators 210, 212 is also configurable, e.g., based on controlsignals from control unit 202. By configuring and re-configuring thepolarity of comparators 210, 212, the logic signals from comparators210, 212 can be made similar for identifying both the ON state and theOFF state of power switches 216 and 218. Comparators 210, 212 may beconfigured to have a first polarity when the respective power switch 216or 218 is ON and configured to have a second polarity when therespective power switch 216 or 218 is OFF, wherein the first polarity isdifferent than the second polarity. Thus, each of first comparator 210and second comparator 212 are configurable with either the firstthreshold or the second threshold based on one or more control signalsfrom control unit 202. This polarity toggling of comparators 210 or 212can simplify logic signals in system 200.

Comparators 210 and 212 operate in a similar and complementary fashionon the high-side and the low-side. First comparator 210 is configured tooutput a first logic signal in response to the gate-to-source voltage ofhigh-side power switch 216 being greater than the first threshold whenhigh-side power switch 216 is ON and to output a second logic signal inresponse to the gate-to-source voltage of high-side power switch 216being less than the second threshold when high-side power switch 216 isOFF. Similarly, second comparator 212 is configured to output a thirdlogic signal in response to the gate-to-source voltage of low-side powerswitch 218 being greater than the first threshold when low-side powerswitch 218 is ON and to output a fourth logic signal in response to thegate-to-source voltage of low-side power switch 218 being less than thesecond threshold when low-side power switch 218 is OFF. Absence of afirst or second logic signal from first comparator 210 during aswitching cycle may indicate a fault associated with first comparator210 and absence of a third or fourth logic signal from second comparator212 during the switching cycle may indicate a fault associated withsecond comparator 212.

Half-bridge driver circuit 204 is configured to turn high-side powerswitch 216 and the low-side power switch ON and OFF in a complementaryfashion. Accordingly, comparators 210 and 212 also operate in acomplementary fashion. Thus, with a half-bridge configuration, firstcomparator 210 is configured to have a first polarity when high-sidepower switch 216 is ON (e.g., when low-side power switch 218 is OFF) andconfigured to have a second polarity when high-side power switch 216 isOFF (e.g., when high-side power switch is ON), wherein the firstpolarity is different than the second polarity. Second comparator 212 isconfigured to have the first polarity when low-side power switch 218 isON (e.g., when high side power 216 switch is OFF) and configured to havethe second polarity when the low-side power switch 218 is OFF (e.g.,when high-side power switch 216 is ON).

System 200 may comprise a circuit for controlling one phase of amulti-phase electric motor, such as a motor used within a vehicle. Inorder to control the motor, a circuit may comprise a plurality of drivercircuits, e.g., similar to half-bridge driver circuit 204, configured tocontrol a plurality of half-bridges. The plurality of half-bridges isconfigured to control the multi-phase electric motor.

FIG. 3 is a circuit diagram showing three half-bridges arranged tocontrol operation of an electric motor 320. Power switches 304A and 306Adefine a first half-bridge, power switches 304B and 306B define a secondhalf-bridge, and power switches 304C and 306C define a thirdhalf-bridge. Each half-bridge may be controlled by a half-bridge drivercircuit similar to half-bridge driver circuit 204 of FIG. 2 . Separatedrivers (similar to driver 106 of FIG. 1 ) could also be used for eachpower switch shown in FIG. 3 .

FIGS. 4A-4D are timing diagrams illustrating one or more aspects of thisdisclosure. FIGS. 4A and 4B show some example faults that may be definedby the absence of an expected logic signal from a comparator accordingto this disclosure.

As shown in FIG. 4A, a driver 106 may deliver signals to a power switch116 to control the ON/OFF state of power switch 116 as defined by graphline 402. Graph line 404 defines gate-to-source monitoring thresholdswhereby less than 1.2 Volts is an OFF threshold and greater than 6.5Volts is an ON threshold. The gate-to-source voltage over power switch116 is shown in graph line 406, and one example output of agate-to-source comparator 110 of driver 106 is shown in graph line 408.As can be seen in FIG. 4A, expected output 40 are periodic logic signalsindicating an ON state followed by an OFF state. However, output 42defines the absence of an expected logic signal for a turn ON, which canidentify a latent fault indicating that the output of comparator 110 isnot necessarily reliable. In such a situation, control unit 102 mayrespond with appropriate action, such as by issuing a maintenance alert,or possibly disabling operation of the power switch until maintenancecan be performed.

FIG. 4B is another timing diagram showing an example fault that can beidentified from a missing logic pulse from a comparator during an OFFtransition. In FIG. 4B, a driver 106 may deliver signals to a powerswitch 116 to control the ON/OFF state of power switch as defined bygraph line 412. Graph line 414 defines gate-to-source monitoringthresholds whereby less than 1.2 Volts is an OFF threshold and greaterthan 6.5 Volts is an ON threshold. In the example shown in FIG. 4B, thegate-to-source voltage over power switch 106 is shown in graph line 416,and one example output of gate-to-source comparator 110 is shown ingraph line 418. As can be seen in FIG. 4B, expected output 44 areperiodic logic signals indicating an ON state followed by an OFF state.However, output 46 defines the absence of an expected logic signal for aturn OFF, which can identify a latent fault indicating that the outputof comparator 110 is not necessarily reliable. In such a situation,control unit 102 may respond with appropriate action, such as by issuinga maintenance alert, or possibly disabling operation of the power switchuntil maintenance can be performed.

FIG. 4C illustrates faults that can be attributed to a faulty drivercircuit (as opposed to a faulty comparator). In FIG. 4C, a driver 106may deliver signals to a power switch 116 to control the ON/OFF state ofpower switch as defined by graph line 422. Graph line 424 definesgate-to-source monitoring thresholds whereby less than 1.2 Volts is anOFF threshold and greater than 6.5 Volts is an ON threshold. Thegate-to-source voltage over the power switch is shown in graph line 426,and one example output of gate-to-source comparator 110 is shown ingraph line 428. As can be seen in FIG. 4C at location 47 of graph line428, driver output does not reach a high level (i.e., does not exceed6.5 volts) within a defined amount of time for a turn ON transition,which may indicate problems with the driver. Alternatively, as can beseen in FIG. 4C at location 48 of graph line 428, driver output does notreach a low level (i.e., does not go below 1.5 volts) within a definedamount of time for turn OFF transition, which may indicate problems withthe driver. The faults shown in FIG. 4C may cause a controller todisable the driver until maintenance can be performed, otherwise, thepower switch may be destroyed by improper drive signals.

In contrast to FIGS. 4A-4C, FIG. 4D shows operation of a differentsystem that does not make use of comparators that are configured asdescribed herein. Rather, the system operation shown in FIG. 4D mayutilize separate comparators to monitor an upper “turn on” threshold ofe.g., 6.5 Volts and to monitor a lower “turn off” threshold of e.g., 1.2Volts. In this case, a driver circuit may deliver signals to a powerswitch to control the ON/OFF state of power switch as defined by graphline 432. Graph line 434 defines gate-to-source monitoring thresholdsused by two different comparators whereby less than 1.2 Volts is an OFFthreshold checked by a comparator and greater than 6.5 Volts is an ONthreshold checked by a different comparator. The gate-to-source voltageover the power switch is shown in graph line 436. As can be seen in FIG.4D, a first gate-to-source comparator signal 438 is defined by a firstcomparator to identify when the gate-to-source voltage is above 6.5Volts and a second gate-to-source comparator signal 440 is defined by asecond comparator to identify when the gate-to-source voltage is below1.2 Volts and a second. Not only does the operation shown in FIG. 4Drequire an additional comparator for each power switch relative to thetechniques of this disclosure, but signal processing is more complicatedrelative to the periodic logic signals expected according to theexamples shown in FIGS. 4A and 4B.

In the diagrams of 4A and 4B, two scenarios are depicted in which thepower switch gate-source monitoring circuitry may be stuck and cannot beused anymore for proper detection power switch functionality. Accordingto this disclosure, a single voltage comparator is used instead of twoindependent monitoring circuitries for the gate-source voltage of apower switch.

As shown in FIG. 4A, in an ON state (expected gate-source voltage above6.5V), the gate-source comparator output stage is checked after theturn-on time. In this case, a low level may indicate that the powerswitch is correctly turned-on and gate-source voltage is higher than6.5V. Moreover, in this case, a high level may indicate an under-voltagecondition, in which case the power switch cannot be reliably turned ON,and an error is reported to the control unit to take the proper action.

As shown in FIG. 4B, in an OFF state (expected gate-source voltage below1.2V), the voltage comparator output is checked after the turn-off time.In this case, a low level indicates that the power switch is correctlyturned-off such that gate-source voltage is lower than 1.2V. A highlevel indicates over-voltage condition, the power switch cannot bereliably turned ON, and an error may be reported to the control unit totake the proper action

In order to allow periodic self-checks of this monitoring feature usinga single comparator, the turn-on and turn-off time windows are used.During these times the power switch gate voltage is ramping up (e.g.,for turn-on) or down (e.g., for turn-off). By using a single comparatorwith inverted polarity:

-   -   In power switch-ON state, a failure is qualified by a        gate-source voltage lower than the comparator threshold    -   In power switch-OFF state, a failure is qualified by a        gate-source voltage higher than the comparator threshold,        Correct monitor functionality can be achieved with a comparator        output that always indicates a high level (e.g., logic high)        when the gate voltage properly ramps up or down. In this way,        whenever a low-high transition is not present on the comparator        output (which may be checked by digital logic located within        driver 106 or within drivers 206 and 208) this lack of an        expected logic pulse can be interpreted as a malfunction of the        monitoring feature, latent fault detection can be triggered, and        signaled from the driver to the control unit to indicate that        the respective monitor feature is not reliable.

For a three-phase electric motor application like that shown in FIG. 3 ,e.g., with six power switches to be controlled, the circuit monitoringof this disclosure may result in a reduction from twelve gate-sourcemonitoring comparators to only six, and a built-in periodic self-test ofthe monitoring feature without switching OFF the monitoring feature. Thedescribed solutions of this disclosure may also achieve additionaladvantages. For example, the techniques may use the actual comparatorcircuitry also for the periodic self-check, such that no additionalswitching of the reference voltages or comparator inputs are needed toforce a functional check of the monitors. The described circuits mayalso achieve a much faster reaction time than conventional monitoringtechniques, and the described circuits can be used as a safety mechanismensuring that all faults are detected within the fault tolerant timeinterval. In case the detection is taking place during every switchingcycle during operation of a power switch, and the self-test can only beused to detect multiple faults, where the fault tolerant time is muchhigher.

By toggling the polarity of the comparator (or comparators) whenchanging the thresholds of the comparator, the expected logic signalsmay comprise a pulse that identifies turn on and a similar pulse thatidentifies turn off. Thus, by toggling the polarity of the comparator(or comparators) when changing the threshold, the same type of logicpulse can be created when gate-to-source voltage exceeds Ton and whengate-to-source voltage falls below Toff. It is also possible toimplement the techniques without changing polarity of the comparator (orcomparators), but in this case, the control unit would need to beprogrammed to identify logic high as the expected logic pulse whencomparing to the first threshold Ton and logic low as the expected logicpulse when comparing to the second threshold Toff. Toggling the polarityof the comparator (or comparators) when changing the threshold, thus,can simplify logic or programming that may otherwise needed in thecontrol unit that controls the driver circuit(s).

Power switches described herein (e.g., power switches 116, 216, 218,304A-304C, and 306A-306C) may each comprise a power transistor, such asa metal oxide semiconductor field effect transistor (MOSFET). The MOSFETmay be formed in silicon, in which case the MOSFET may be called asilicon MOSFET. Alternatively, the MOSFET may be formed in anothersemiconductor material, such as silicon carbide (SiC) or gallium nitride(GaN), in which case the MOSFET may be called a SiC MOSFET or a GaNMOSFET. Indeed, the techniques of this disclosure may be especiallyuseful for monitoring MOSFETS that arc used for controlling athree-phase electric motor, such as those used in vehicles. Thetechniques of this disclosure may also work with other types oftransistors, such as bipolar gate transistors (BGTs), in which case thegate-to-source monitoring would comprise monitoring of a gate to emittervoltage of the BGTs.

FIGS. 5 and 6 are flow diagrams according to this disclosure. FIG. 5will be described from the perspective of driver circuit 106 of FIG. 1although other circuits or devices may also perform the technique shownin FIG. 5 . As shown in FIG. 5 , driver circuit 106 controls a powerswitch 116 to ON (501), such as by delivering sufficient voltage to thegate of power switch 116. Based on signals from control unit 102, drivercircuit 106 sets the threshold of comparator 110 to a first threshold“Ton” (502) and in some examples, driver also sets the polarity ofcomparator 110 to positive “+” (503). During the expected switch-ONcycle, driver 106 checks the gate-to-source voltage of the power switchvia comparator 110 (504). In particular, comparator 110 compares thegate-to-source voltage of power switch 116 to the “Ton” threshold andoutputs an expected logic signal when the gate-to-source voltage exceedsthe “Ton” threshold. If the expected logic signal is present, thencircuit operation is verified, and everything is OK (OK branch of 504).However, if the expected logic signal is absent, then circuit operationis unverified such that there could be a problem (FAULT branch of 504).In the case of a FAULT due to a missing logic signal, the control unit102 may issue an alert for maintenance (FAULT branch of 504).

As further shown in FIG. 5 , driver circuit 106 then controls a powerswitch 116 to OFF (505), such as by delivering lower voltage to the gateof power switch 116. Based on signals from control unit 102, drivercircuit 106 sets the threshold of comparator 110 to a second threshold“Toff” (506) and in some examples, driver also sets the polarity ofcomparator 110 to negative “−” (507). During the expected switch-OFFcycle, driver 106 checks the gate-to-source voltage of the power switchvia comparator 110 (508). In particular, comparator 110 compares thegate-to-source voltage of power switch 116 to the “Toff” threshold andoutputs an expected logic signal when the gate-to-source voltage fallsbelow the “Toff” threshold. If the expected logic signal is present,then circuit operation is verified, and everything is OK (OK branch of508). However, if the expected logic signal is absent, then circuitoperation is unverified such that there could be a problem (FAULT branchof 508). In the case of a FAULT due to a missing logic signal, thecontrol unit 102 may issue an alert for maintenance.

FIG. 6 is a flow diagram that is similar to FIG. 5 , but FIG. 6 showscomplementary operation of two different driver circuits that control ahigh-side switch and a low-side switch. FIG. 6 will be described fromthe perspective of half-bridge driver circuit 204 of FIG. 2 , althoughother circuits or devices may also perform the technique shown in FIG. 6. As shown in FIG. 2 , half bridge-driver circuit 204 comprises ahigh-side driver circuit 206 for controlling high-side power switch 216and a low-side driver circuit 208 for controlling low-side power switch218. High-side driver circuit 206 and low-side driver circuit 208 maycomprise separate circuits formed on separate semiconductor substrates,or in some examples, high-side driver circuit 206 and low-side drivercircuit 208 may comprise a single integrated circuit.

As shown in FIG. 6 , half-bridge driver circuit 204 controls high-sidepower switch 216 to ON and low side power switch to OFF (601), such asby high-side driver circuit 206 delivering sufficient voltage to thegate of high-side power switch 216 and low-side driver circuit 208delivering low voltage to the gate of low-side power switch 218. Basedon signals from control unit 202, high-side driver circuit 206 sets thethreshold of comparator 210 to a first threshold “Ton” (602) and in someexamples, high-side driver circuit 206 also sets the polarity ofcomparator 210 to positive “+” (603). Similarly and in a complementaryfashion relative to operation of high-side driver circuit 206, based onthe signals from control unit 202, low-side driver circuit 208 sets thethreshold of comparator 212 to a second threshold “Toff” (604) and insome examples, low-side driver circuit 206 also sets the polarity ofcomparator 212 to negative “−” (605).

During the expected switch-ON cycle of high-side power switch 216,high-side driver 206 checks the gate-to-source voltage of the powerswitch via comparator 210 (606). In particular, comparator 210 comparesthe gate-to-source voltage of high-side power switch 216 to the “Ton”threshold and outputs an expected logic signal when the gate-to-sourcevoltage exceeds the “Ton” threshold. If the expected logic signal ispresent, then circuit operation is verified, and everything is OK (OKbranch of 606). However, if the expected logic signal is absent, thencircuit operation is unverified such that there could be a problem(FAULT branch of 606). In the case of a FAULT due to a missing logicsignal, the control unit 202 may issue an alert for maintenance (FAULTbranch of 606).

The expected switch-ON cycle of high-side power switch 216 correspondsto an expected switch-OFF cycle of low-side power switch 218.Accordingly, low-side driver 208 checks the gate-to-source voltage oflow-side power switch via comparator 212 (607). In particular,comparator 212 compares the gate-to-source voltage of low-side powerswitch 218 to the “Toff” threshold and outputs an expected logic signalwhen the gate-to-source voltage falls below the “Toff” threshold. If theexpected logic signal is present, then circuit operation is verified,and everything is OK (OK branch of 607). However, if the expected logicsignal is absent, then circuit operation is unverified such that therecould be a problem (FAULT branch of 607). In the case of a FAULT due toa missing logic signal, the control unit 202 may issue an alert formaintenance (FAULT branch of 607).

As further shown in FIG. 5 , half-bridge driver circuit 204 thencontrols high-side power switch 216 to OFF and low side power switch toON (608), such as by high-side driver circuit 206 delivering low voltageto the gate of high-side power switch 216 and low-side driver circuit208 delivering sufficient voltage to the gate of low-side power switch218.

Based on signals from control unit 202, high-side driver circuit 206sets the threshold of comparator 210 to the second threshold “Toff”(609) and in some examples, high-side driver circuit 206 also sets thepolarity of comparator 210 to negative “−” (610). Similarly and in acomplementary fashion relative to operation of high-side driver circuit206, based on the signals from control unit 202, low-side driver circuit208 sets the threshold of comparator 212 to the first threshold “Ton”(611) and in some examples, low-side driver circuit 206 also sets thepolarity of comparator 212 to positive “−” (612).

During the expected switch-OFF cycle of high-side power switch 216,high-side driver 206 checks the gate-to-source voltage of the powerswitch via comparator 210 (613). In particular, comparator 210 comparesthe gate-to-source voltage of high-side power switch 216 to the “Toff”threshold and outputs an expected logic signal when the gate-to-sourcevoltage falls below the “Toff” threshold. If the expected logic signalis present, then circuit operation is verified, and everything is OK (OKbranch of 613). However, if the expected logic signal is absent, thencircuit operation is unverified such that there could be a problem(FAULT branch of 613). In the case of a FAULT due to a missing logicsignal, the control unit 202 may issue an alert for maintenance (FAULTbranch of 613).

The expected switch-OFF cycle of high-side power switch 216 correspondsto an expected switch-ON cycle of low-side power switch 218.Accordingly, low-side driver 208 checks the gate-to-source voltage oflow-side power switch via comparator 212 (614). In particular,comparator 212 compares the gate-to-source voltage of low-side powerswitch 218 to the “Ton” threshold and outputs an expected logic signalwhen the gate-to-source voltage exceeds the “Ton” threshold. If theexpected logic signal is present, then circuit operation is verified,and everything is OK (OK branch of 614). However, if the expected logicsignal is absent, then circuit operation is unverified such that therecould be a problem (FAULT branch of 614). In the case of a FAULT due toa missing logic signal, the control unit 202 may issue an alert formaintenance (FAULT branch of 614).

The following clauses may illustrate one or more aspects of thedisclosure.

Clause 1—A driver circuit configured to control a power switch, thedriver circuit comprising: an output pin configured to deliver signalsto a gate of the power switch to control an ON/OFF state of the powerswitch; and a comparator configured to compare a gate-to-source voltageof the power switch to a first threshold when the power switch is ON andto compare the gate-to-source voltage of the power switch to a secondthreshold when the power switch is OFF.

Clause 2—The driver circuit of clause 1, wherein the comparator isconfigurable with either the first threshold or the second thresholdbased on one or more control signals from a control unit.

Clause 3—The driver circuit of clause 1 or 2, wherein the comparator isconfigured to output a first logic signal in response to thegate-to-source voltage being greater than the first threshold when thepower switch is ON and to output a second logic signal in response tothe gate-to-source voltage being less than the second threshold when thepower switch is OFF.

Clause 4—The driver circuit any of clauses 1-3, wherein the absence of alogic signal from the comparator during a switching cycle of the powerswitch indicates a fault associated with the comparator.

Clause 5—The driver circuit any of clauses 1-4, wherein the comparatoris configured to have a first polarity when the power switch is ON andconfigured to have a second polarity when the power switch is OFF,wherein the first polarity is different than the second polarity.

Clause 6—A driver circuit configured to control a high-side power switchand a low-side power switch arranged in a half-bridge, the drivercircuit comprising: a first output pin configured to deliver high-sidesignals to a gate of the high-side power switch to control an ON/OFFstate of the high-side power switch; a second output pin configured todeliver low-side signals to a gate of the low-side power switch tocontrol an ON/OFF state of the low-side power switch; a first comparatorconfigured to compare a gate-to-source voltage of the high-side powerswitch to a first threshold when the high-side power switch is ON and tocompare the gate-to-source voltage of the high-side power switch to asecond threshold when the high-side power switch is OFF; and a secondcomparator configured to compare a gate-to-source voltage of thelow-side power switch to the first threshold when the low-side powerswitch is ON and to compare the gate-to-source voltage of the low-sidepower switch to the second threshold when the low-side power switch isOFF.

Clause 7—The driver circuit of clause 6, wherein the first and secondcomparators are each configurable with either the first threshold or thesecond threshold based on one or more control signals from a controlunit.

Clause 8—The driver circuit of claim 6 or 7, wherein the firstcomparator is configured to output a first logic signal in response tothe gate-to-source voltage of the high-side power switch being greaterthan the first threshold when the high-side power switch is ON and tooutput a second logic signal in response to the gate-to-source voltageof the high-side power switch being less than the second threshold whenthe high-side power switch is OFF, and wherein the second comparator isconfigured to output a third logic signal in response to thegate-to-source voltage of the low-side power switch being greater thanthe first threshold when the low-side power switch is ON and to output afourth logic signal in response to the gate-to-source voltage of thelow-side power switch being less than the second threshold when thelow-side power switch is OFF.

Clause 9—The driver circuit any of clauses 6-8, wherein an absence of afirst or second logic signal from the first comparator during aswitching cycle indicates a fault associated with the first comparatorand wherein an absence of a third or fourth logic signal from the secondcomparator during the switching cycle indicates a fault associated withthe second comparator.

Clause 10—The driver circuit any of clauses 6-9, wherein the driver isconfigured to turn the high-side power switch and the low-side powerswitch ON and OFF in a complementary fashion, wherein the firstcomparator is configured to have a first polarity when the high-sidepower switch is ON and configured to have a second polarity when thehigh-side power switch is OFF, wherein the first polarity is differentthan the second polarity, and wherein the second comparator isconfigured to have the first polarity when the low-side power switch isON and configured to have the second polarity when the low-side powerswitch is OFF.

Clause 11—The driver circuit of any of clauses 6-10, further comprisinga plurality of driver circuits configured to control a plurality ofhalf-bridges.

Clause 12—The driver circuit of clause 11, wherein the plurality ofhalf-bridges is configured to control a multi-phase electric motor.

Clause 13—A system comprising: a control unit; and a driver circuitconfigured to receive control signals from the control unit and tocontrol a half-bridge based on the control signals, wherein thehalf-bridge includes a high-side power switch and a low-side powerswitch, the driver circuit comprising: a first output pin configured todeliver high-side signals to a gate of the high-side power switch tocontrol an ON/OFF state of the high-side power switch; a second outputpin configured to deliver low-side signals to a gate of the low-sidepower switch to control an ON/OFF state of the low-side power switch; afirst comparator configured to compare a gate-to-source voltage of thehigh-side power switch to a first threshold when the high-side powerswitch is ON and to compare the gate-to-source voltage of the high-sidepower switch to a second threshold when the high-side power switch isOFF; and a second comparator configured to compare a gate-to-sourcevoltage of the low-side power switch to the first threshold when thelow-side power switch is ON and to compare the gate-to-source voltage ofthe low-side power switch to the second threshold when the low-sidepower switch is OFF.

Clause 14—The system of clause 13, the system further comprising thehigh-side power switch and the low-side power switch.

Clause 15—The system of clause 13 or 14, wherein the control unit isconfigured to disable the half-bridge in response to receiving anindication from either the first comparator or second comparator thateither the low-side power switch or the high-side power switch is stuckin an ON state.

Clause 16—The system of any of clauses 13-15, wherein the control unitis configured to issue a maintenance alert for the system in response toreceiving an indication of a fault from either the first comparator orthe second comparator.

Clause 17—The system of any of clauses 13-16, wherein an absence of anexpected logic signal from either the first comparator or the secondcomparator during a switching cycle indicates a fault.

Clause 18—The system of any of clause claim 13-17, further comprising aplurality of driver circuits configured to control a plurality ofhalf-bridges, wherein the plurality of half-bridges is configuredcontrol a multi-phase electric motor.

Clause 19—The system of claim 18, the system further comprising themulti-phase electric motor.

Clause 20—A method of controlling a power switch, the method comprising:delivering signals to a gate of the power switch to control an ON/OFFstate of the power switch; receiving a first threshold from a controlunit to configure a comparator; comparing, via the comparator, agate-to-source voltage of the power switch to the first threshold whenthe power switch is ON; receiving a second threshold from the controlunit to configure the comparator, wherein the second threshold isdifferent than the first threshold; and comparing, via the comparator,the gate-to-source voltage of the power switch to the second thresholdwhen the power switch is OFF

Clause 21—The method of clause 20, further comprising: outputting afirst logic signal in response to the gate-to-source voltage beinggreater than the first threshold when the power switch is ON; andoutputting a second logic signal in response to the gate-to-sourcevoltage being less than the second threshold when the power switch isOFF.

Clause 22—The method of clause 21, wherein an absence of the first orsecond logic signal from the comparator during a switching cycleindicates a fault associated with the comparator.

Clause 23—The method of any of clauses 20-22, further comprising:receiving an indication of a first polarity to configure polarity of thecomparator during an ON state of the power switch; and receiving anindication of a second polarity to configure polarity of the comparatorduring an OFF state of the power switch.

Various features and aspects have been described in this disclosure.These and other features and aspects are within the scope of thefollowing claims.

The invention claimed is:
 1. A driver circuit configured to control apower switch, the driver circuit comprising: an output pin configured todeliver signals to a gate of the power switch to control an ON/OFF stateof the power switch; and a comparator configured to compare agate-to-source voltage of the power switch to a first threshold when thepower switch is ON and to compare the gate-to-source voltage of thepower switch to a second threshold when the power switch is OFF, whereinan absence of a logic signal from the comparator during a switchingcycle of the power switch indicates a fault associated with thecomparator.
 2. The driver circuit of claim 1, wherein the comparator isconfigurable with either the first threshold or the second thresholdbased on one or more control signals from a control unit.
 3. The drivercircuit of claim 1, wherein the comparator is configured to output afirst logic signal in response to the gate-to-source voltage beinggreater than the first threshold when the power switch is ON and tooutput a second logic signal in response to the gate-to-source voltagebeing less than the second threshold when the power switch is OFF. 4.The driver circuit of claim 1, wherein the comparator is configured bythe driver circuit based on control signals from a control unit todefine a first polarity when the power switch is ON and to define asecond polarity when the power switch is OFF, wherein the first polarityis different than the second polarity.
 5. A driver circuit configured tocontrol a high-side power switch and a low-side power switch arranged ina half-bridge, the driver circuit comprising: a first output pinconfigured to deliver high-side signals to a gate of the high-side powerswitch to control an ON/OFF state of the high-side power switch; asecond output pin configured to deliver low-side signals to a gate ofthe low-side power switch to control an ON/OFF state of the low-sidepower switch; a first comparator configured to compare a gate-to-sourcevoltage of the high-side power switch to a first threshold when thehigh-side power switch is ON and to compare the gate-to-source voltageof the high-side power switch to a second threshold when the high-sidepower switch is OFF; and a second comparator configured to compare agate-to-source voltage of the low-side power switch to the firstthreshold when the low-side power switch is ON and to compare thegate-to-source voltage of the low-side power switch to the secondthreshold when the low-side power switch is OFF, wherein an absence of afirst logic signal or a second logic signal from the first comparatorduring a switching cycle indicates a fault associated with the firstcomparator and wherein an absence of a third logic signal or a fourthlogic signal from the second comparator during the switching cycleindicates a fault associated with the second comparator.
 6. The drivercircuit of claim 5, wherein the first and second comparators are eachconfigurable with either the first threshold or the second thresholdbased on one or more control signals from a control unit.
 7. The drivercircuit of claim 5, wherein the first comparator is configured to outputthe first logic signal in response to the gate-to-source voltage of thehigh-side power switch being greater than the first threshold when thehigh-side power switch is ON and to output h second logic signal inresponse to the gate-to-source voltage of the high-side power switchbeing less than the second threshold when the high-side power switch isOFF, and wherein the second comparator is configured to output the thirdlogic signal in response to the gate-to-source voltage of the low-sidepower switch being greater than the first threshold when the low-sidepower switch is ON and to output h fourth logic signal in response tothe gate-to-source voltage of the low-side power switch being less thanthe second threshold when the low-side power switch is OFF.
 8. Thedriver circuit of claim 5, wherein the driver circuit is configured toturn the high-side power switch and the low-side power switch ON and OFFin a complementary fashion, wherein the first comparator is configuredby the driver circuit based on control signals from a control unit todefine a first polarity when the high-side power switch is ON and todefine a second polarity when the high-side power switch is OFF, whereinthe first polarity is different than the second polarity, and whereinthe second comparator is configured by the driver circuit based oncontrol signals from the control unit to define the first polarity whenthe low-side power switch is ON and to define the second polarity whenthe low-side power switch is OFF.
 9. The driver circuit of claim 5,further comprising a plurality of driver circuits configured to controla plurality of half-bridges.
 10. The driver circuit of claim 9, whereinthe plurality of half-bridges is configured to control a multi-phaseelectric motor.
 11. A system comprising: a control unit; and a drivercircuit configured to receive control signals from the control unit andto control a half-bridge based on the control signals, wherein thehalf-bridge includes a high-side power switch and a low-side powerswitch, the driver circuit comprising: a first output pin configured todeliver high-side signals to a gate of the high-side power switch tocontrol an ON/OFF state of the high-side power switch; a second outputpin configured to deliver low-side signals to a gate of the low-sidepower switch to control an ON/OFF state of the low-side power switch; afirst comparator configured to compare a gate-to-source voltage of thehigh-side power switch to a first threshold when the high-side powerswitch is ON and to compare the gate-to-source voltage of the high-sidepower switch to a second threshold when the high-side power switch isOFF; and a second comparator configured to compare a gate-to-sourcevoltage of the low-side power switch to the first threshold when thelow-side power switch is ON and to compare the gate-to-source voltage ofthe low-side power switch to the second threshold when the low-sidepower switch is OFF, wherein an absence of an expected logic signal fromeither the first comparator or the second comparator during a switchingcycle indicates a fault.
 12. The system of claim 11, further comprisingthe high-side power switch and the low-side power switch.
 13. The systemof claim 11, wherein the control unit is configured to disable thehalf-bridge in response to the fault.
 14. The system of claim 11,wherein the control unit is configured to issue a maintenance alert forthe system in response to the fault.
 15. The system of claim 11, furthercomprising a plurality of driver circuits configured to control aplurality of half-bridges, wherein the plurality of half-bridges isconfigured to control a multi-phase electric motor.
 16. The system ofclaim 15, further comprising the multi-phase electric motor.
 17. Amethod of controlling a power switch, the method comprising: deliveringsignals to a gate of the power switch to control an ON/OFF state of thepower switch; receiving a first threshold from a control unit toconfigure a comparator; comparing, via the comparator, a gate-to-sourcevoltage of the power switch to the first threshold when the power switchis ON; receiving a second threshold from the control unit to configurethe comparator, wherein the second threshold is different than the firstthreshold; and comparing, via the comparator, the gate-to-source voltageof the power switch to the second threshold when the power switch isOFF, wherein an absence of a first or second logic signal from thecomparator during a switching cycle indicates a fault associated withthe comparator.
 18. The method of claim 17, further comprising:outputting the first logic signal in response to the gate-to-sourcevoltage being greater than the first threshold when the power switch isON; and outputting the second logic signal in response to thegate-to-source voltage being less than the second threshold when thepower switch is OFF.
 19. The method of claim 17, further comprising:receiving, from a control unit, an indication of a first polarity toconfigure a polarity of the comparator during an ON state of the powerswitch; and receiving, from the control unit, an indication of a secondpolarity to configure the polarity of the comparator during an OFF stateof the power switch.